1. Technical Field
The disclosure relates to a transition mode (TM) power factor corrector (PFC) power converter adapted to switch from a DCM (discontinuous current mode) to a CCM (continuous current mode) under high load.
2. Description of the Related Art
Transition mode (also known as quasi resonant) boost power factor corrector devices (PFC) function in a discontinuous current mode (DCM) and have a high efficiency. However, for a same average current value, in DCM the power transfer current reaches higher peak values of than in a switching power converter functioning in a continuous current mode (CCM). This is due to the fact that the transition mode peculiarity of requiring a nullification of the current in the inductor at every switching cycle has the drawback of producing a current ripple of amplitude that is about twice the value of the waveform of the average current.
In a PFC (power factor correction) power converter there is a current loop through a boost inductor from where a loop signal is derived for implementing an effective and reliable control of the output DC voltage. In transition mode, a constant on-time control timer of the switch of the boost inductor is generally employed for regulating the power transfer to track load requirements. Commonly, the on-time interval of the switch is set in function of the output voltage. Therefore, if the load remains constant the on-time remains constant too.
Switching from the discontinuous current mode of a TM-PFC circuit to a continuous current mode of operation for reducing the ripple amplitude specially under heavy load conditions is desirable.
The ability to switch from a DCM (discontinuous current mode) to a CCM (continuous current mode) under high load conditions generally requires a complex control circuitry, given that the common technique, based on an on-time control timer of the switch of the boost inductor, relies on a null initial current for obtaining a current proportional to the instantaneous input voltage and thus is unsuitable.
The document, Publ. No. U.S. 2013/0141056-A1, addresses a specific problem of difference between current loop gains when the PFC power converter operates in a CCM (continuous current mode) and in a DCM (discontinuous current mode).
An effective, though much simplified control method for reliably and efficiently switching a from DCM to CCM a transition mode (TM) power factor corrector (PFC) power converter is highly desired.